Vendors who sell Legendary gear all sell them with comparable stats. Crucible gear bought with Crucible marks have equal Light bonuses (+18 to be specific) with Vanguard gear bought with Vanguard marks. The same can be said of the three other vendors with their own reputation, Dead Orbit, Future War Cult, and New Monarchy. To earn reputation with these three in order to purchase legendary gear you could get at the standard Crucible and Vanguard vendors, you must purchase a bond and then wear it as you progress through story missions, Strikes and Crucible matches, and all reputation points are appointed to that vendor.